J. Org. Chem. 1992,57,4963-4970
4963
Reaction of Tricoordinate Phosphorus Compounds with Organophosphorus Pseudohalogens. 1. Desulfurization and Deoxygenation of Oxophosphoranesulfenyl Chlorides. Scope and Mechanism+ E. Krawczyk, J. Mikolajczak, A. Skowrofiska,* and J. Michalski* Polish Academy of Sciences, Centre of Molecular a n d Macromolecular Studies, Sienkiewicza 112, 90-363 L a g , Poland Received April 26, 1990 (Revised M a n u s c r i p t Received F e b r u a r y 17, 1992)
The reaction of oxophosphoranesulfenylchlorides RR’P(O)SCl2 with PIncompounds has been investigated. Its mechanisticfeaturea have been elucidated by variable-temperature31PNMR spectroecopyand stereochemical changes at Pw and Pnlphosphorus cfnters. These studies show that in all cases phosphonium intermediates containing the sulfur bridge >P(O)-S-Pt Cl- are formed. Depending on electronic and steric factors and reaction conditions, this primary phosphonium salt either decomposes by nucleophilic attack of the chloride counterion on the plyphoryl center (desulfurization pathway) or is transformed into the isomeric phosphonium salt >P(S)-0-PtC1-. The latter decomposes by the attack of the chloride anion on the thiophosphoryl center (deoxygenation pathway). 31PNMR studies fully corroborated the observed stereochemical changes. Scheme I
Introduction
As a part of a research program on the chemistry and stereochemistry of thio- and selenophosphates, detailed studies have been undertaken on the reactions of pseudohalogens such as thiocyanogen (SCN),,’ phosphoryl disulfides [R,P(O)S],,2 phosphoryl diselenides [R,P(O)Se],,2t3 and oxophosphoranesulfenylhalides RzP(0)SX2>4 with tricoordinate phosphorus compounds. Organophosphorus disulfides RR’P(O)SSP(O)RR’ 1 display a variety of properties similar to those of elemental halogens, and hence the term pseudohalogens or halogenoids has been applied to theme5 The pseudohalogen behaviour of disulfides 1 was first described by Foss.‘j Oxophosphoranesulfenylchlorides RR’P(O)SC12, representing pseudohalogenohalogens, were obtained for the first time, and studied, in this The high affinity of tricoordinate phosphorus compounds toward oxygen and sulfur is based on their tendency to form a strong phwphoryl P=O or thiophosphoryl P==S“double”bond. Desulfurization and deoxygenation reactions by tricoordinate phosphorus compounds are widely used in organic synthesi~.~Little attention has been paid to the systems containing both “active”0 and S atoms. Harpp et al. observed preferential desulfurization of thiolosulfonates RSOzSR by tris(diethy1amino)phosphine.1° Barton et al. described preferential deoxygenation of sulfenyl esters RS-OR with the triphenylphosphine.” Early observations of similar reactions in phosphorus chemistry with parallel desulfurization and deoxygenation of bis(phosphiny1) disulfides 1 by triphenylphosphine have been reported by Edmundson.12 Michalski and Skowrofiska et al. observed deoxygenation, desulfurization and dealkylation of oxophosphoranesulfenyl chlorides 2 by trialkyl phosphite^.^ We describe the results of systematic studies of the reaction between chiral and nonchiral oxophosphoranesulfenyl chlorides 2 and tricoordinate phosphorus compounds. In these investigations it was essential to combine chemical and stereochemical observations with those derived from variable-temperature 31PNMR experiments. Our aim was to disclose mechanistic features of deoxygenation and desulfurization processes of importance for applications in synthetic organophosphorus chemistry. Results and Discussion For our experimental observations and the mechanistic Dedicated to Professor Frank H. Westheimer on the occasion of his 80th birthday.
0
1:
iP .,.R ,,
CI-PR”,
B
.it feature of these reactions it is advantageous to examine Scheme I. This scheme provides a general description of (1)Burski, J.; Kieszkowski, J.; Michalski, J.; Pakulski, M.; Skowroheka, A. Tetrahedron 1983,39,4175and references cited therein. (2)Skowrobska,A.; Krawczyk, E.; Burski, J. Phosphorus Sulfur Relat. Elem. 1983,18,233 and references cited therein. (3)Dembhki, R.; Krawczyk, E.; Skowrofiska,A. Phosphorus Sulfur Relat. Elem. 1988,35,345. (4) (a) Michalski, J.; Skowrobska, A. J. Chem. SOC. C 1970,703. (b) Krawiecka, B.; Michalski, J.; Mikdajczak, J.; Mikdajczyk, M.; Omelaiiczuk, J.; Skowrofiska, A. J. Chem. SOC., Chem. Commun. 1974, 630. (c) Omelaiczuk, J.; Kielbasifiski, P.; Michalski, J.; Mikdajczak, J.; Mikdajczyk, M.; Skowrobska, A. Tetrahedron 1975,31,2809. (d) Michalski, J.; Skowroiiska, A.; Bodalski, R. In Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis; Verkade, J. G., Quin, L. D., Eds.; VCH Publishers: New York, 1987;Chapter 8. (5)(a) Moeller, T.Inorganic Chemistry; J. Wiley: New York, 1952. (b) Huheey, J. E. Inorganic Chemistry; Harper and Row: New York, 1978; p 677. (6)Fosa, 0.Acta Chem. Scand. 1947,1, 307. (7)Borecka, B.: Michalski, J. Roczniki Chem. 1957. 31, 1167. Michalski, J.; Skowroheka, A. Chem. Ind. 1958,1199. Michalski, J.; Pliszka-Krawiecka, B.; Skowrobska, A. Roczniki Chem. 1963,37,1479. (8) (a) Michaleki, J. Bull. SOC. Chim. Fr. 1963,ll and references cited therein. (b)Markowska, A.; Michalski, J. Roczniki Chem. 1964,38,1141. (c) Borecka, B.; Jezierska, B.; Bluj, S.; Michalski, J. Bull. Acad. Polon. Sci., Ser. Sci. Chim. 1974,22,201. (9)(a) Mukaiyama, T.;Takei, H. Topics in Phosphorus Chemistry; J. Wiley and Sons: New York, 1976; Vol. VIII, pp 587-645. (b) Corey, E.J.; Brunella, D. J. Tetrahedron Lett. 1976,3409. (c) Mukaiyama, T.; Matseuda, H.; Suzuki, M. Tetrahedron Lett. 1970,1901. (d) Cadogan, J. I. Acc. Chem. Res. 1972, 5, 303. (e) Cadogan, J. I. G. Organophosphorus Reagents in Organic Synthesis; Academic Press: New York, 1979; pp 269-380. (10)Harpp, D.N.; Gleason, J. G.; Ash, D. K. J. Org. Chem. 1971,36, 322.
0022-326319211957-4963$03.00/0 0 1992 American Chemical Society
Krawczyk et al.
4964 J. Org. Chem., Vol. 57, No.18,1992 Table I. Derulfuriution and Deoxygenation of Sulfenyl Chloride 2 by PIi1Compounds 3 desulfurization entry
sulfenyl chloride 2 (EtO)2P(O)SCl (EtO)EtP(O)SCl
1 2
Pm compd 3
(%a)
(MeaCCH20)JP (MeaCCH20)aP
100 100
deoxygenation (96)
0 0
3 cis, trans
(EtO)2P(O)SCl
4
100
&P :;-oPn
trans
(EtO)EtP(O)SCI
5
100 &P :;O - PL
trans 100 &P-OPh
cis, trans 100
7
0
cis, trans 0 9 10 11
(EtO)Q(O)SCl (EtO)iP(O)SCl (EtO)EtP(O)SCl
12 13
(EtO)EtP(O)SCl (EtO)2P(O)SCl
100 94 96 95
cis, trans 92 85 60
8 15 40
60
40
60 58
40 42
cis, trans 15
(EtO)EtP(O)SCl
16 17
cis, trans 10 (OY 5 0
18 19 20
90 (100)” 95 100
‘Reaction wiu carried out at -100 OC.
the desulfurization (path a) and deoxygenation (pathe b-d) reactions and contains an essence of our mechanistic interpretation. The pathways a and b-d are representative only for those systems in which ligands at tricoordinate phosphorus are resistant to dealkylation or desilylation. When an alkoxy group OR” is attached to the Pm center the izomeric monothiopyrophosphates 8 and 9 are formed. Formation of 8 results from dealkylation of the intermediate A. 0
O-R”’
n
CI-
R ‘P-S2PR/ [I id R” A
- ”*, R‘
0
0
,P-s-P
